Field of the Invention
The present invention relates to an apparatus for detecting variations in inclination or acceleration of an article and to generate a signal representative of the position of the article, and more particularly relates to an apparatus associated with the walking beam of a sucker-rod type pump for providing a signal which assists detection of fluid pound in wells employing sucker-rod pumping units.
Although the invention will be described in relation to its preferred pump controlling environment, it will be understood that there is a need for the apparatus in other environments. The apparatus will be referred to herein as an inclinometer, which inclinometer is capable of producing an output signal related to changes in angular positions of an article and/or changes in acceleration of an article. The inclinometer of the present invention performs these functions with a high degree of repeatability and with substantially infinite life at an extremely low price and is sufficiently accurate to perform its intended function. Known inclinometers, such as a Humphrey pendulum, use a simple pendulum which rotates a potentiometer and is relatively expensive, is highly accurate and repeatable, but has a limited life. Known prior art accelerometers can also be used as inclinometers but have limited life due to wear at pivot points, bearings, and wear to the potentiometer. The comparative cost of the above known devices are approximately six to ten times that of the inclinometer of the present invention.
The preferred use of the apparatus of the present invention is for detecting pound in wells employing sucker-rod pumping units.
Sucker-rod type pumping units are widely used in the petroleum industry in order to recover fluid from wells extending into subterranean formations. Such units include a sucker-rod string which extends into the well and means at the surface for an up and down movement of the rod string in order to operate a downhole pump. Typical of such units are the so called "beam-type" pumping units having the sucker-rod string suspended at the surface of the well from a structure consisting of a Samson post and a walking beam pivotally mounted on the Samson post. The sucker-rod string normally is connected at one end of the walking beam and the other end of the walking beam is connected to a prime mover such as a motor through a suitable crank and pitman connection. In this arrangement the walking beam and the sucker-rod string are driven in a reciprocal mode by the prime mover.
A variety of malfunctions such as worn pumps, broken sucker-rods, split tubing, and stuck pump valves can interrupt the pumping of fluid from a well. Such malfunctions can be caused by normal wear and tear on the equipment, by the nature of the fluid being pumped or they could be caused by abnormal pumping conditions.
One abnormal pumping condition which is fairly common is known as "fluid pound". Fluid pound occurs when the well is pumped-off, i.e., when fluid is withdrawn from the well at a rate greater than the rate at which the fluid enters the well from the formation. When this occurs, the working cylinder of the downhole pump is only partially filled during an upstroke of the plunger and on the downstroke of the plunger strikes or "pounds" the fluid in the working cylinder causing severe jarring of the entire pumping unit. This causes damage to the rod string and to the surface equipment and may lead to failure of the pumping unit.